This is a great thread, because it demonstrates the current major
contradiction between what nutritional "experts" say and what is
obvious biochemically (known from the molecular-level evidence).  If
you eat a substance with a relatively high unsaturated fatty acid
content, it may very well "go bad" quickly, whereas I've had coconut
oil that was still fine more than 2 years after purchase (it is about
92% saturated fatty acids).  Keep in mind that the new oils are
combinations of totally hyrodgenated oils (like cottonseed, which is
cheap) and a cheap oil that is rich in PUFAs, such as safflower - in
this way, they can say that it is free of trans fatty acids, or "trans
fats," as some incorrectly call them.  This is not a healthy
substance, but it is likely that the hydrogenated oil fraction is the
healthiest substance in this kind of "food," because it does not go
rancid.  Rancidity is called lipid peroxidation on the molecular
level, and when this happens, not only can vital biomolecules be
damaged or destroyed, but the immune system will act them, thinking
they are a foreign "invading" substance.  This is not the case for
saturated fatty acids, which act to stop lipid peroxidation.

In fact, I will eat some "junk food" these days, so long as it has
almost all saturated fat in it, or no fat at all.  For instance,
Snackwell makes a fat free devil's food cookie, and a local
supermarket has a chocolate mint cookie that has 9 grams of fat per
serviing, 7 of which are saturated.  By eating food that goes rancid
quickly, you are assuring that some damage will be done via lipid
peroxidation reactions.  Even if it seems find before you eat it, it
can still be subject to lipid peroxidation inside your body.  Do a
google search for in vivo lipid peroxidation if you want to see all
the evidence now available.  On my free site, I present some of the
best evidence:

http://groups.msn.com/TheScientificDebateForum-/

You can ask me questions on the formums there, if you have any.  Don't
be fooled by old preconceptions that are scientifically invalid.  Much
of the old nutritional ideas have been refuted by new, molecular-level
evidence - but you won't hear about it in the mainstream media due to
the mindset of the people who determine which stories to "run with."
They don't think you would understand this new evidence, and they may
not understand it either.  As I often tell people, you can do your own
experiment by getting a dozen adult mice or rats and feeding them a
30% canola and fish oil diet, while another group of mice are fed
hydrogenated coconut oil.  See which group lives longer.